Interactions of Phase Transformations and Plasticity: Session 9
Program Organizers: Valery Levitas, Iowa State University

Friday 2:00 PM
July 14, 2017
Room: Water Tower
Location: Hyatt Regency Chicago

Session Chair: Steven Mates, National Institute of Standards and Technology

2:00 PM  
Correlation between Deformation Texture and Martensitic Transformation in TWIP/TRIP Steels on multiscale: Marton Benke1; Mate Sepsi1; Erzsebet Nagy1; Peter Pekker1; Valeria Mertinger1; 1University of Miskolc
    In the present manuscript, the texture variation of γ austenite, ε martensite and α’ martensite phases are investigated in FeMn(Cr) steels exhibiting both TWIP and TRIP behaviour during uniaxial tensile tests. Samples of three steels with varying Cr content were subjected to tensile tests till fracture on different temperatures ranging from room temperature, at which ε martensite and γ austenite are stable to 453 K, where only γ austenite was present prior to tensile stressing. The developed texture of ε martensite, α’ martensite and γ austenite was examined on multiscale, by TEM orientation mapping, Electron Backscattered Diffraction (EBSD) orientation mapping and X-ray-diffraction pole figure measurements. Correlations between the developed textures and the formation of the martensitic phases are discussed.

2:20 PM  
Molecular Dynamics Simulation of Dislocation Induced Phase Transformations: Hao Chen1; Liming Xiong1; Levitas Valery1; 1IOWA STATE UNIVERSITY
    It is known from experiment that superposition of plastic deformation on high pressure can significantly reduce phase transformation pressure for various materials. Molecular dynamics simulations are performed to investigate the interaction between dislocations and phase transformations in silicon. Dislocation pile up against the grain boundary produces strong stress tensor concentrator and induces phase transformation from the other side of a boundary at pressure significantly lower than under hydrostatic conditions. Also, three most stable ⟨110⟩ tilt boundaries are investigated. Results show that phase transformation pressure can be also greatly reduced for all boundaries. The type of phase transformation depends on the interatomic potential used. For the Stillinger-Weber potential, amorphous silicon can be produced. For the Tersoff potential, phase transformation pressure for silicon II can be strongly reduced.

2:40 PM  
Constitutive Modeling of Martensitic Transformation in Twinning Induced Plasticity Steels Subjected to Thermomechanical Load: Rashid Khan1; Tasneem Pervez2; Omar Al-Abri2; Sayyad Qamar2; 1Al Imam University; 2Sultan Qaboos University
    Advanced high strength steels (AHSS) cover a vast range of applications where large deformation of a material is desired. Their successful implementation is due to an optimum combination of strength and formability. Twinning induced plasticity (TWIP) steel has excellent strength-cum-formability among AHSS. Stress assisted martensitic transformation found to be principal reason behind an enhancement of these properties. This work is aimed to investigate an elastic-plastic behavior of TWIP steel; undergoes slip, and mechanical twinning subjected to thermomechanical load. Initially, constitutive model is developed through kinematic decomposition of austenite into intermediate configurations. Thermodynamic framework is used to formulate driving potential for twinning. The developed model is then numerically implemented into finite element software ABAQUS through user-defined subroutine. Finally, finite element simulations are performed for single and polycrystal austenite subjected to different loads. It is found that in tension, twin deformation plays a dominant role, while reverse is observed in compression.

3:00 PM  
Influence of Ti2Cu Precipitates on the Functional Fatigue in TiNiCu Films: Lars Bumke1; Christoph Chluba1; Rodrigo Lima de Miranda2; Julian Strobel1; Torben Dankwort1; Lorenz Kienle1; Eckhard Quandt1; 1University of Kiel; 2Acquandas GmbH
     Applications like elastocaloric cooling require shape memory alloys with high fatigue resistance (>108 cycles) and narrow hysteresis. A good crystallographic compatibility described by the co-factor conditions is detrimental for a small hysteresis width, whereas its influence on the functional fatigue is still not fully understood. Besides the good crystallographic compatibility between the B2 and B19 phases in TiNiX alloys, Ti-rich precipitations like Ti2Cu (space group I4/mmm) seem to be beneficial [1], since they promote the reversible transformations. To investigate the influence of the Ti2Cu and Ti2Ni precipitates, sputtered amorphous Ti53.7Ni24.7Cu21.6 thin films were fabricated and heat treated. Cyclic superelastic fatigue test under tension revealed a strong correlation between annealing temperature and functional fatigue. The influence of the microstructure on the fatigue behaviour and elastocaloric properties with respect to annealing temperature, will be discussed.[1] Chluba et al., Science, 348 (2015), 1004-1007.

3:15 PM  
A 3D Finite Strain Constitutive Model of Shape Memory Alloys Incorporating Transformation Induced Plasticity under Cyclic Loading: Lei Xu1; Theocharis Baxevanis2; Dimitris Lagoudas1; 1Texas A&M University; 2University of Houston
    A three-dimensional phenomenological constitutive model for shape memory alloys (SMAs) considering transformation induced plasticity (TRIP) in the finite strain regime is proposed in this work. The infinitesimal strain assumption considered in existing models from the literature is inaccurate for SMAs in the presence of large TRIP strains accumulated during cyclic thermomechanical loading. The proposed finite strain model is constructed based on logarithmic strain measure for large deformation analysis. The martensite volume fraction, transformation strain, and TRIP strain are used to characterize the inelastic evolution features exhibited by SMAs during cyclic thermomechanical loading. An objective integration procedure is also developed for the implementation of the model. Boundary value problems such as a bar and a torque tube under both pseudo-elastic and actuation cyclic loadings are performed to test the capabilities of the newly proposed model.

3:30 PM Break